1. Technical Field of the Invention
This invention relates generally to portable handheld digital audio systems and more particularly to integrated circuits comprising a handheld audio system.
2. Description of Related Art
As is known, handheld digital audio systems are becoming very popular. Such systems include digital audio players/recorders that record and subsequently playback MP3 files, WMA files, etc. Such digital audio players/recorders may also be used as digital dictaphones and file transfer devices. Further expansion of digital audio players/recorders includes providing a frequency modulation (FM) radio receiver such that the device offers FM radio reception.
While digital audio players/recorders are increasing their feature sets, the increase in feature sets has been done in a less than optimal manner. For instance, with the inclusion of an FM receiver in a digital audio player/recorder, the FM receiver is a separate integrated circuit from the digital audio player/recorder chip set, or IC. As such, the FM receiver integrated circuit (IC) functions completely independently of the digital audio player/recorder IC, even though both ICs include some common functionality.
Further, FM receivers function to convert a radio frequency signal into a complex baseband signal that is decoded, or demodulated, to produce a decoded baseband signal. A channel separation function splits the decoded baseband signal into a left channel signal and a right channel signal. As with any integrated circuit implemented using CMOS (complimentary metal oxide semiconductor) technology, errors in timing, signal recapture, crystal frequency variations, and variations from part to part occur. To account for such errors, FM receivers include error correcting circuit to adjust the decoded baseband signal once it is produced. While this technical reduces the above described adverse affects, it requires a fairly complex circuit implementation and addresses the problem in a passive cause and affect manner.
Four papers teach FM receivers that address at least one of the above mentioned issues. The four papers include, “A 10.7-MHz IF-to-Baseband Sigma-Delta A/D Conversion System for AM/FM Radio Receivers” by Eric Van Der Zwan, et. al. IEEE Journal of Solid State Circuits, VOL. 35, No. 12, December 2000; “A fully Integrated High-Performance FM Stereo Decoder” by Gregory J. Manlove et. al, IEEE Journal of Solid State Circuits, VOL. 27, No. 3, March 1992; “A 5-MHz IF Digital FM Demodulator”, by Jaejin Park et. al, IEEE Journal of Solid State Circuits, VOL. 34, No. 1, January 1999; and “A Discrete-Time Bluetooth Receiver in a 0.13 μm Digital CMOS Process”, by K. Muhammad et. al, ISSCC2004/Session 15/Wireless Consumer ICs/15.1, 2004 IEEE International Solid-State Circuit Conference.
Therefore, a need exists for a method and apparatus for non-passive radio decoding that is optimized to function with a digital audio player/recorder.